1 use super::{truncate_i32_to_i16, truncate_i32_to_i8}; 2 use crate::{ 3 prelude::*, 4 runtime::vm::{GcHeap, GcStore, VMGcRef}, 5 store::{AutoAssertNoGc, StoreOpaque}, 6 vm::GcArrayLayout, 7 AnyRef, ExternRef, HeapType, RootedGcRefImpl, StorageType, Val, ValType, 8 }; 9 use core::fmt; 10 use wasmtime_environ::VMGcKind; 11 12 /// A `VMGcRef` that we know points to a `array`. 13 /// 14 /// Create a `VMArrayRef` via `VMGcRef::into_arrayref` and 15 /// `VMGcRef::as_arrayref`, or their untyped equivalents 16 /// `VMGcRef::into_arrayref_unchecked` and `VMGcRef::as_arrayref_unchecked`. 17 /// 18 /// Note: This is not a `TypedGcRef<_>` because each collector can have a 19 /// different concrete representation of `arrayref` that they allocate inside 20 /// their heaps. 21 #[derive(Debug, PartialEq, Eq, Hash)] 22 #[repr(transparent)] 23 pub struct VMArrayRef(VMGcRef); 24 25 impl fmt::Pointer for VMArrayRef { 26 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 27 fmt::Pointer::fmt(&self.0, f) 28 } 29 } 30 31 impl From<VMArrayRef> for VMGcRef { 32 #[inline] 33 fn from(x: VMArrayRef) -> Self { 34 x.0 35 } 36 } 37 38 impl VMGcRef { 39 /// Is this `VMGcRef` pointing to a `array`? 40 pub fn is_arrayref(&self, gc_heap: &(impl GcHeap + ?Sized)) -> bool { 41 if self.is_i31() { 42 return false; 43 } 44 45 let header = gc_heap.header(&self); 46 header.kind().matches(VMGcKind::ArrayRef) 47 } 48 49 /// Create a new `VMArrayRef` from the given `gc_ref`. 50 /// 51 /// If this is not a GC reference to an `arrayref`, `Err(self)` is 52 /// returned. 53 pub fn into_arrayref(self, gc_heap: &impl GcHeap) -> Result<VMArrayRef, VMGcRef> { 54 if self.is_arrayref(gc_heap) { 55 Ok(self.into_arrayref_unchecked()) 56 } else { 57 Err(self) 58 } 59 } 60 61 /// Create a new `VMArrayRef` from `self` without actually checking that 62 /// `self` is an `arrayref`. 63 /// 64 /// This method does not check that `self` is actually an `arrayref`, but 65 /// it should be. Failure to uphold this invariant is memory safe but will 66 /// result in general incorrectness down the line such as panics or wrong 67 /// results. 68 #[inline] 69 pub fn into_arrayref_unchecked(self) -> VMArrayRef { 70 debug_assert!(!self.is_i31()); 71 VMArrayRef(self) 72 } 73 74 /// Get this GC reference as an `arrayref` reference, if it actually is an 75 /// `arrayref` reference. 76 pub fn as_arrayref(&self, gc_heap: &(impl GcHeap + ?Sized)) -> Option<&VMArrayRef> { 77 if self.is_arrayref(gc_heap) { 78 Some(self.as_arrayref_unchecked()) 79 } else { 80 None 81 } 82 } 83 84 /// Get this GC reference as an `arrayref` reference without checking if it 85 /// actually is an `arrayref` reference. 86 /// 87 /// Calling this method on a non-`arrayref` reference is memory safe, but 88 /// will lead to general incorrectness like panics and wrong results. 89 pub fn as_arrayref_unchecked(&self) -> &VMArrayRef { 90 debug_assert!(!self.is_i31()); 91 let ptr = self as *const VMGcRef; 92 let ret = unsafe { &*ptr.cast() }; 93 assert!(matches!(ret, VMArrayRef(VMGcRef { .. }))); 94 ret 95 } 96 } 97 98 impl VMArrayRef { 99 /// Get the underlying `VMGcRef`. 100 pub fn as_gc_ref(&self) -> &VMGcRef { 101 &self.0 102 } 103 104 /// Clone this `VMArrayRef`, running any GC barriers as necessary. 105 pub fn clone(&self, gc_store: &mut GcStore) -> Self { 106 Self(gc_store.clone_gc_ref(&self.0)) 107 } 108 109 /// Explicitly drop this `arrayref`, running GC drop barriers as necessary. 110 pub fn drop(self, gc_store: &mut GcStore) { 111 gc_store.drop_gc_ref(self.0); 112 } 113 114 /// Copy this `VMArrayRef` without running the GC's clone barriers. 115 /// 116 /// Prefer calling `clone(&mut GcStore)` instead! This is mostly an internal 117 /// escape hatch for collector implementations. 118 /// 119 /// Failure to run GC barriers when they would otherwise be necessary can 120 /// lead to leaks, panics, and wrong results. It cannot lead to memory 121 /// unsafety, however. 122 pub fn unchecked_copy(&self) -> Self { 123 Self(self.0.unchecked_copy()) 124 } 125 126 /// Get the length of this array. 127 pub fn len(&self, store: &StoreOpaque) -> u32 { 128 store.unwrap_gc_store().array_len(self) 129 } 130 131 /// Read an element of the given `StorageType` into a `Val`. 132 /// 133 /// `i8` and `i16` fields are zero-extended into `Val::I32(_)`s. 134 /// 135 /// Does not check that this array's elements are actually of type 136 /// `ty`. That is the caller's responsibility. Failure to do so is memory 137 /// safe, but will lead to general incorrectness such as panics and wrong 138 /// results. 139 /// 140 /// Panics on out-of-bounds accesses. 141 pub fn read_elem( 142 &self, 143 store: &mut AutoAssertNoGc, 144 layout: &GcArrayLayout, 145 ty: &StorageType, 146 index: u32, 147 ) -> Val { 148 let offset = layout.elems_offset + index * ty.byte_size_in_gc_heap(); 149 let data = store.unwrap_gc_store_mut().gc_object_data(self.as_gc_ref()); 150 match ty { 151 StorageType::I8 => Val::I32(data.read_u8(offset).into()), 152 StorageType::I16 => Val::I32(data.read_u16(offset).into()), 153 StorageType::ValType(ValType::I32) => Val::I32(data.read_i32(offset)), 154 StorageType::ValType(ValType::I64) => Val::I64(data.read_i64(offset)), 155 StorageType::ValType(ValType::F32) => Val::F32(data.read_u32(offset)), 156 StorageType::ValType(ValType::F64) => Val::F64(data.read_u64(offset)), 157 StorageType::ValType(ValType::V128) => Val::V128(data.read_v128(offset)), 158 StorageType::ValType(ValType::Ref(r)) => match r.heap_type().top() { 159 HeapType::Extern => { 160 let raw = data.read_u32(offset); 161 Val::ExternRef(ExternRef::_from_raw(store, raw)) 162 } 163 HeapType::Any => { 164 let raw = data.read_u32(offset); 165 Val::AnyRef(AnyRef::_from_raw(store, raw)) 166 } 167 HeapType::Func => todo!("funcrefs inside gc objects not yet implemented"), 168 otherwise => unreachable!("not a top type: {otherwise:?}"), 169 }, 170 } 171 } 172 173 /// Write the given value into this array at the given offset. 174 /// 175 /// Returns an error if `val` is a GC reference that has since been 176 /// unrooted. 177 /// 178 /// Does not check that `val` matches `ty`, nor that the field is actually 179 /// of type `ty`. Checking those things is the caller's responsibility. 180 /// Failure to do so is memory safe, but will lead to general incorrectness 181 /// such as panics and wrong results. 182 /// 183 /// Panics on out-of-bounds accesses. 184 pub fn write_elem( 185 &self, 186 store: &mut AutoAssertNoGc, 187 layout: &GcArrayLayout, 188 ty: &StorageType, 189 index: u32, 190 val: Val, 191 ) -> Result<()> { 192 debug_assert!(val._matches_ty(&store, &ty.unpack())?); 193 194 let offset = layout.elem_offset(index, ty.byte_size_in_gc_heap()); 195 let mut data = store.unwrap_gc_store_mut().gc_object_data(self.as_gc_ref()); 196 match val { 197 Val::I32(i) if ty.is_i8() => data.write_i8(offset, truncate_i32_to_i8(i)), 198 Val::I32(i) if ty.is_i16() => data.write_i16(offset, truncate_i32_to_i16(i)), 199 Val::I32(i) => data.write_i32(offset, i), 200 Val::I64(i) => data.write_i64(offset, i), 201 Val::F32(f) => data.write_u32(offset, f), 202 Val::F64(f) => data.write_u64(offset, f), 203 Val::V128(v) => data.write_v128(offset, v), 204 205 // For GC-managed references, we need to take care to run the 206 // appropriate barriers, even when we are writing null references 207 // into the array. 208 // 209 // POD-read the old value into a local copy, run the GC write 210 // barrier on that local copy, and then POD-write the updated 211 // value back into the array. This avoids transmuting the inner 212 // data, which would probably be fine, but this approach is 213 // Obviously Correct and should get us by for now. If LLVM isn't 214 // able to elide some of these unnecessary copies, and this 215 // method is ever hot enough, we can always come back and clean 216 // it up in the future. 217 Val::ExternRef(e) => { 218 let raw = data.read_u32(offset); 219 let mut gc_ref = VMGcRef::from_raw_u32(raw); 220 let e = match e { 221 Some(e) => Some(e.try_gc_ref(store)?.unchecked_copy()), 222 None => None, 223 }; 224 store.gc_store_mut()?.write_gc_ref(&mut gc_ref, e.as_ref()); 225 let mut data = store.gc_store_mut()?.gc_object_data(self.as_gc_ref()); 226 data.write_u32(offset, gc_ref.map_or(0, |r| r.as_raw_u32())); 227 } 228 Val::AnyRef(a) => { 229 let raw = data.read_u32(offset); 230 let mut gc_ref = VMGcRef::from_raw_u32(raw); 231 let a = match a { 232 Some(a) => Some(a.try_gc_ref(store)?.unchecked_copy()), 233 None => None, 234 }; 235 store.gc_store_mut()?.write_gc_ref(&mut gc_ref, a.as_ref()); 236 let mut data = store.gc_store_mut()?.gc_object_data(self.as_gc_ref()); 237 data.write_u32(offset, gc_ref.map_or(0, |r| r.as_raw_u32())); 238 } 239 240 Val::FuncRef(_) => todo!("funcrefs inside gc objects not yet implemented"), 241 } 242 Ok(()) 243 } 244 245 /// Initialize an element in this arrayref that is currently uninitialized. 246 /// 247 /// The difference between this method and `write_elem` is that GC barriers 248 /// are handled differently. When overwriting an initialized element (aka 249 /// `write_elem`) we need to call the full write GC write barrier, which 250 /// logically drops the old GC reference and clones the new GC 251 /// reference. When we are initializing an element for the first time, there 252 /// is no old GC reference that is being overwritten and which we need to 253 /// drop, so we only need to clone the new GC reference. 254 /// 255 /// Calling this method on a arrayref that has already had the associated 256 /// element initialized will result in GC bugs. These are memory safe but 257 /// will lead to generally incorrect behavior such as panics, leaks, and 258 /// incorrect results. 259 /// 260 /// Does not check that `val` matches `ty`, nor that the field is actually 261 /// of type `ty`. Checking those things is the caller's responsibility. 262 /// Failure to do so is memory safe, but will lead to general incorrectness 263 /// such as panics and wrong results. 264 /// 265 /// Returns an error if `val` is a GC reference that has since been 266 /// unrooted. 267 /// 268 /// Panics on out-of-bounds accesses. 269 pub fn initialize_elem( 270 &self, 271 store: &mut AutoAssertNoGc, 272 layout: &GcArrayLayout, 273 ty: &StorageType, 274 index: u32, 275 val: Val, 276 ) -> Result<()> { 277 debug_assert!(val._matches_ty(&store, &ty.unpack())?); 278 let offset = layout.elem_offset(index, ty.byte_size_in_gc_heap()); 279 match val { 280 Val::I32(i) if ty.is_i8() => store 281 .gc_store_mut()? 282 .gc_object_data(self.as_gc_ref()) 283 .write_i8(offset, truncate_i32_to_i8(i)), 284 Val::I32(i) if ty.is_i16() => store 285 .gc_store_mut()? 286 .gc_object_data(self.as_gc_ref()) 287 .write_i16(offset, truncate_i32_to_i16(i)), 288 Val::I32(i) => store 289 .gc_store_mut()? 290 .gc_object_data(self.as_gc_ref()) 291 .write_i32(offset, i), 292 Val::I64(i) => store 293 .gc_store_mut()? 294 .gc_object_data(self.as_gc_ref()) 295 .write_i64(offset, i), 296 Val::F32(f) => store 297 .gc_store_mut()? 298 .gc_object_data(self.as_gc_ref()) 299 .write_u32(offset, f), 300 Val::F64(f) => store 301 .gc_store_mut()? 302 .gc_object_data(self.as_gc_ref()) 303 .write_u64(offset, f), 304 Val::V128(v) => store 305 .gc_store_mut()? 306 .gc_object_data(self.as_gc_ref()) 307 .write_v128(offset, v), 308 309 // NB: We don't need to do a write barrier when initializing a 310 // field, because there is nothing being overwritten. Therefore, we 311 // just the clone barrier. 312 Val::ExternRef(x) => { 313 let x = match x { 314 None => 0, 315 Some(x) => x.try_clone_gc_ref(store)?.as_raw_u32(), 316 }; 317 store 318 .gc_store_mut()? 319 .gc_object_data(self.as_gc_ref()) 320 .write_u32(offset, x); 321 } 322 Val::AnyRef(x) => { 323 let x = match x { 324 None => 0, 325 Some(x) => x.try_clone_gc_ref(store)?.as_raw_u32(), 326 }; 327 store 328 .gc_store_mut()? 329 .gc_object_data(self.as_gc_ref()) 330 .write_u32(offset, x); 331 } 332 333 Val::FuncRef(_) => { 334 // TODO: we can't trust the GC heap, which means we can't read 335 // native VMFuncRef pointers out of it and trust them. That 336 // means we need to do the same side table kind of thing we do 337 // with `externref` host data here. This isn't implemented yet. 338 todo!("funcrefs in GC objects") 339 } 340 } 341 Ok(()) 342 } 343 } 344